Electrical converters are found in many different types of electrical systems. Generally speaking, a converter converts a supply of a first type to an output of a second type. Such conversion can include DC-DC, AC-AC and DC-AC electrical conversions. In some configurations a converter may have any number of DC and AC ‘parts’, for example a DC-DC converter might incorporate an AC-AC converter stage in the form of a transformer.
One example of the use of converters is in inductive power transfer (IPT) systems. IPT systems are a well-known area of established technology (for example, wireless charging of electric toothbrushes) and developing technology (for example, wireless charging of handheld devices on a ‘charging mat’).
IPT systems will typically include an inductive power transmitter and an inductive power receiver. The inductive power transmitter includes a transmitting coil or coils, which are driven by a suitable transmitting circuit to generate an alternating magnetic field. The alternating magnetic field will induce a current in a receiving coil or coils of the inductive power receiver. The received power may then be used to charge a battery, or power a device or some other load associated with the inductive power receiver. Further, the transmitting coil and/or the receiving coil may be connected to a resonant capacitor to create a resonant circuit. A resonant circuit may increase power throughput and efficiency at the corresponding resonant frequency.
Typically, receivers used in IPT systems consist of a power receiving coil and a circuit topology configured to convert the induced power from AC to DC and to regulate the voltage of the power ultimately provided to a load.
A common problem with receivers used in IPT systems is that switched-mode regulators may include a DC inductor. The DC inductor acts as an energy store so that power can be suitably regulated. Such DC inductors can be a bulky circuit component, significantly affecting the total size occupied by the receiver. This can be a particular problem in applications where it is preferable that the receiver be as small as possible (for example, receivers used with mobile devices).
Another problem with known receivers is that they can include a substantial number of components. For switched-mode regulators this can include multiple switches. This adds to the bulk and complexity, and ultimately cost, of the receiver. As there is a growing desire to adopt IPT systems in consumer devices (such as smartphones), such increased bulk, complexity and cost presents a barrier to wide spread adoption that needs to be minimised.